The present invention relates to a movable magnet type linear motor with the purpose of improving motor efficiency and of simplifying the manufacture of the motor.
In recent years, fervent efforts have been made on the development of linear motor.
Japanese Patent Application 10-118358 describes a conventional type linear motor.
Description will be given below on the conventional type linear motor as described above referring to the drawings.
FIG. 14 is a cross-sectional plan view of a conventional type linear motor, and FIG. 15 is a cross-sectional view along the line Axe2x80x94A in FIG. 14.
An inner yoke 1 is designed in form of quadratic prism by laminating a multiple of thin plates 2, each of which is in approximately rectangular shape and has high magnetic permeability. An outer yoke 3 is designed in form of quadratic prism by laminating a multiple of thin plates 4, each of which is in approximately rectangular shape and has high magnetic permeability. Slots 6 and 7 are cut out in axial direction 5, and three magnetic poles 8, 9 and 10 are formed. The surface of the outer yoke 3 having the magnetic poles 8, 9 and 10 is directed toward the inner yoke 1 and a yoke block 12 is formed with a given gap 11 between them. A set of yoke blocks is retained on a base 13 so that the inner yokes are arranged at positions opposite to each other with a given spacing.
Coils 14 are wound around the central magnetic pole 9 so that different magnetic poles are alternately formed at three magnetic poles 8, 9 and 10 of outer yoke 3. The coils 14 are independently wound on two outer yokes 3, and the coils 14 are connected in parallel.
A movable unit 15 comprises a pair of planar permanent magnets 16 and 17 magnetized in opposed directions of the inner yoke 1 and the outer yoke 3, a permanent magnet holder 18, and a shaft 19. The permanent magnets 16 and 17 are fixed by a permanent magnet holder 18 with a given spacing in axial direction so that directions of magnetization are opposite to each other, and these magnets are disposed in the gap 11 between the inner yoke 1 and the outer yoke 3.
Description will be given now on operation of the linear motor with the above arrangement.
A magnetic flux generated from the permanent magnet 16 passes through the gap 11, the inner yoke 1, the gap 11, the permanent magnet 17, the outer yoke 3, and the gap 11 and returns to the permanent magnet 16, and a static magnetic field is generated in the gap 11. In the inner yoke 1 and the outer yoke 3, the magnetic flux circulates in the planes of the thin plates 2 and 4.
When AC current is supplied to the coil 14, different magnetic poles are alternately generated in axial direction at the magnetic poles 8, 9, and 10. By magnetically attracting and repelling action of the permanent magnets 16 and 17 of the movable unit 15, thrust force is generated, which is proportional to the magnitude of electric current flowing through the coil 14 and to magnetic flux density of the permanent magnets 16 and 17. Then, the shaft 19 is reciprocally moved together with the movable unit 15 in synchronization with the frequency of AC current.
The conventional arrangement as described above is advantageous in that the inner yoke 1 and the outer yoke 3 can be manufactured in easier manner. However, planar permanent magnets 16 and 17 are arranged in parallel in the gap 11 between the inner yoke 1 and the outer yoke 3 each designed in form of quadratic prism. When the shaft 19 is disposed at axially rotated position during manufacture, balance is lost in the distance between the permanent magnets 16 and 17 and the inner yoke 1 or the distance between the permanent magnets 16 and 17 and the outer yoke 3. This leads to instability of the thrust force of the linear motor.
To solve the above problems of the conventional example, it is an object of the present invention to provide a linear motor, in which the thrust force of the linear motor is not turned to unstable even when the shaft 19 is disposed at axially rotated position during manufacture and motor efficiency can be improved and yokes can be manufactured in easier manner.
Also, when the permanent magnets 16 and 17 are disposed at deviated positions closer to the inner yoke 1 or to the outer yoke 3 during manufacture, balance is lost in the distance between the permanent magnets 16 and 17 and the inner yoke 1 or in the distance between the permanent magnets 16 and 17 and the other yoke 3. Thus, the force to directly attract the permanent magnets 16 and 17 toward the inner yoke 1 or the outer yoke 3 is increased. As a result, sliding loss is increased on the bearings 20 via the movable unit 15 and the shaft 19.
It is another object of the present invention to provide a linear motor, in which, even when permanent magnets are disposed at deviated positions closer to the inner yoke or the outer yoke during manufacture, the force to directly attract the permanent magnets toward the inner yoke or the outer yoke is not increased, and the motor efficiency is improved, and the yokes can be manufactured in easier manner.
To solve these problems, the linear motor according to the present invention comprises a movable unit in cylindrical shape and having the central axis at the intersection of X-axis and Y-axis, an inner yoke arranged on inner side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in parallel to one of X-axis or Y-axis, an outer yoke arranged on outer side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in the same direction as the thin plates of the inner yoke, and a pair of permanent magnets magnetized in a direction to connect the inner yoke with the outer yoke and mounted on the movable unit to be retained in a gap between the inner yoke and the outer yoke.
As a result, even when the shaft is disposed at axially rotated position during the manufacture, the thrust force of the linear motor is not turned to unstable. Iron loss of the inner yoke and the outer yoke is reduced. Motor efficiency is improved, and this facilitates the manufacture of the linear motor.
Also, the present invention provides the linear motor as described above, wherein a pair of permanent magnets magnetized in radial direction around the central axis are arranged with a given spacing in parallel to the central axis so that directions of magnetization are opposite to each other, and the magnets being retained in a gap between the inner yoke and the outer yoke.
With such an arrangement, even when the permanent magnets are disposed at deviated positions closer to the inner yoke or the outer yoke, the force to directly attract the permanent magnets toward the inner yoke or the outer yoke is not increased.
Further, the present invention provides the linear motor as described above, wherein the inner yoke is formed by laminating a multiple of thin plates of the same shape and the same dimension, and the outer yoke is formed by laminating a multiple of thin plates of the same shape and the same dimension.
As a result, it is possible to manufacture the linear motor in easier manner.
Also, the present invention provides the linear motor as described above, wherein radius of curvature of inner periphery of the outer yoke is equal to radius of curvature of inner periphery of the slot, and radius of curvature of outer periphery of the outer yoke is equal to radius of curvature of outer periphery of the slot, and radius of curvature of outer periphery of the outer yoke or the slot is greater than the radius of curvature of the inner periphery of the outer yoke or the slot.
As a result, it is possible to design the linear motor in compact size.
Further, the present invention provides the linear motor as described above, wherein outer peripheral end of each of the outermost sides in laminating direction of the thin plates of the inner yoke and an end surface of the permanent magnet are on a line, which connects inner peripheral end of each of the outermost sides in laminating direction of the thin plates of the outer yoke with the intersection of X-axis and Y-axis.
Accordingly, it is possible to reduce the amount of magnets.
Also, the present invention provides the linear motor as described above, wherein two inner yokes are arranged symmetrically with respect to Y-axis, and the two inner yokes are integrated by two inner yoke support members disposed inside the inner yoke and positioned separately in direction of Y-axis.
As a result, the inner yoke can be integrated to a single component, and this facilitates the assembling procedure.
Further, the present invention provides the linear motor as described above, wherein two outer yokes are arranged symmetrically with respect to Y-axis, and the two outer yokes are integrated by two outer yoke support members disposed on each of the outermost sides in laminating direction of the thin plates of the outer yokes.
As a result, the outer yokes can be integrated to a single component, and this facilitates the assembling procedure.
Also, the present invention provides a linear motor, which comprises a movable unit in cylindrical shape having central axis thereof at the intersection of X-axis and Y-axis, an inner yoke arranged on inner side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in parallel to one of X-axis or Y-axis, an outer yoke arranged on outer side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in the same direction as the thin plates of the inner yoke, a base in planar shape for retaining the inner yoke and the outer yoke, a cylinder mounted on the base as to be positioned at the center of X-axis and Y-axis, a piston designed to retain a pair of permanent magnets magnetized in a direction to connect the inner yoke with the outer yoke and retained in a gap between the inner yoke and the outer yoke, provided at forward end of a shaft integrated with the movable unit and placed in the cylinder, and a spring mounted on the shaft.
As a result, even when the permanent magnets are disposed at deviated position closer to the inner yoke or the outer yoke, the force to directly attract the permanent magnets toward the inner yoke or the outer yoke is not increased. Therefore, sliding loss between the piston and the cylinder is also not increased, and this facilitates the manufacture of the linear motor.
Further, the present invention provide a linear motor, which comprises a movable unit in cylindrical shape and having the central axis at the intersection of X-axis and Y-axis, an inner yoke arranged on inner side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in parallel to one of X-axis or Y-axis, an outer yoke arranged on outer side of the movable unit with a given spacing in radial direction of the movable unit, being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability arranged in the same direction as the thin plates of the inner yoke, and forming a first magnetic pole, a second magnetic pole and a third magnetic pole by arranging two slots cut out in the laminating direction of the thin plates, a coil wound on the second magnetic pole of the outer yoke and forming alternately different magnetic poles at the first magnetic pole, the second magnetic pole and the third magnetic pole, a base in planar shape for retaining the inner yoke and the outer yoke, bearings mounted on the base to be positioned at the center of X-axis and Y-axis, a pair of permanent magnets magnetized in a direction to connect the inner yoke with the outer yoke and mounted on the movable unit to be retained in a gap between the inner yoke and the outer yoke with a given spacing in parallel to the central axis so that directions of magnetization are opposite to each other. Because the movable unit is designed in cylindrical shape, even when the shaft is disposed at axially rotated position during manufacture, thrust force of the linear motor is not turned to unstable. Iron loss in the inner yoke and the outer yoke is reduced, and motor efficiency is improved, and this facilitates the manufacture of the linear motor.
According to another aspect of the present invention, a pair of permanent magnets magnetized in radial direction around the central axis are retained in a gap between the inner yoke and the outer yoke with a given spacing in parallel to the central axis so that directions of magnetization are opposite to each other. Even when the permanent magnets are disposed at deviated positions closer to the inner yoke or the outer yoke during manufacture, the force to directly attract the permanent magnets toward the inner yoke or the outer yoke is not increased, and sliding loss on the sliding portions can be reduced.
According to still another aspect of the present invention, the inner yoke is formed by thin plates of the same shape and the same dimension, and the outer yoke is formed by thin plates of the same shape and the same dimension. Because the inner yoke and the outer yoke can be easily manufactured, this facilitates the manufacture of the linear motor.
According to still another aspect of the present invention, radius of curvature of inner periphery of the outer yoke is equal to radius of curvature of inner periphery of the slot, and radius of curvature of outer periphery of the outer yoke is equal to radius of curvature of outer periphery of the slot. Radius of curvature of outer periphery of the outer yoke or the slot is greater than the radius of curvature of inner periphery of the outer yoke or the slot. This makes it possible to design the linear motor in compact size.
According to still another aspect of the present invention, it is designed in such manner that outer periphery of each of the outermost sides in laminating direction of the thin plates of the inner yoke and an end surface of the permanent magnets are on a line, which connects inner periphery of each of the outermost sides in laminating direction of the thin plates of the outer yoke with the intersection of X-axis and Y-axis. As a result, the amount of magnets can be reduced.
According to still another aspect of the present invention, two inner yokes are disposed symmetrically with respect to Y-axis, and the two inner yokes are integrated by two inner yoke support members provided inside the two inner yokes and positioned separately in direction of Y-axis. As a result, the two inner yokes can be integrated to a single component, and this facilitates the assembling procedure.
According to still another aspect of the present invention, two outer yokes are disposed symmetrically with respect to Y-axis, and the two outer yokes are integrated by two outer yoke support members arranged at each of the outermost sides in laminating direction of the thin plates of the two outer yokes. As a result, the two outer yokes are integrated to a single component, and this facilitates the assembling of the linear motor.
According to still another aspect of the present invention, the linear motor comprises a movable unit of cylindrical shape having central axis thereof at the intersection of X-axis and Y-axis, an inner yoke arranged on inner side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability in parallel to one of X-axis or Y-axis, an outer yoke arranged on outer side of the movable unit with a given spacing in radial direction of the movable unit and being formed by laminating a multiple of thin plates each in approximately rectangular shape and having high magnetic permeability in the same direction as the thin plates of the inner yoke, a base in planar shape for retaining the inner yoke and the outer yoke, a cylinder mounted on the base as to be positioned at the center of X-axis and Y-axis, a pair of permanent magnets magnetized in a direction to connect the inner yoke with the outer yoke and arranged on the movable unit to be retained in a gap between the inner yoke and the outer yoke with a given spacing in parallel to the central axis so that directions of magnetization are opposite to each other, a piston disposed at forward end of a shaft integrated with the movable unit and placed in the cylinder, and a spring mounted on the shaft. Even when the permanent magnets are disposed at deviated position closer to the inner yoke or the outer yoke, the force to directly attract the permanent magnets toward the inner yoke or the outer yoke is not increased. Therefore, sliding loss between the piston and the cylinder is not increased, and this facilitates the manufacture of the linear motor.